Described methods and systems provide in-situ leakage current testing of battery cells in battery packs even while these packs operate. Specifically, an external electrical current is discontinued through a tested battery cell using a node controller, to which the tested battery cell is independently connected. Changes in the open circuit voltage (OCV) are then detected by the node controller for a set period time. Any voltage change, associated with taking the tested cell offline, is compensated by one or more other cells in the battery pack. The overall pack current and voltage remains substantially unchanged (based on the application demands), while the in-situ leakage current testing is initiated, performed, and/or completed. The OCV changes are then used to determine the leakage current of the tested cell and, in some examples, to determine the state of health of this cell and/or adjust the operating parameters of this cell.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for on-demand in-situ leakage current testing of selected battery cells in a battery pack, the method comprising: discontinuing an external cell current through a first battery cell of a first battery node using a first node controller, wherein: the first battery cell is selected from multiple battery cells in the battery pack for purposes of determining leakage current, the first node controller is connected in series with one or more additional node controllers of the battery pack, the one or more additional node controllers control operation of one or more additional cells in the battery pack, and the one or more additional cells continue to charge or discharge according to a power compensation profile to ensure that the power output of the battery pack is substantially unchanged while the external cell current through the first battery cell is discontinued; obtaining cell data from the first battery cell using the first node controller while discontinuing the external cell current through the first battery cell; determining the leakage current of the first battery cell based on the cell data; and reestablishing the external cell current through the first battery cell, using the first node controller and switching the one or more additional cells back from the power compensation profile, using the one or more additional node controllers, such that the power output of the battery pack remains substantially unchanged.
2. The method of claim 1 , wherein discontinuing the external cell current through the first battery cell is performed when a state of charge (SOC) of the first battery cell is within a predetermined range.
3. The method of claim 1 , wherein discontinuing the external cell current through the first battery cell is triggered by a battery pack controller, communicatively coupled to the first node controller, and wherein discontinuing the external cell current through the first battery cell is triggered based on at least one of operating history of the first battery cell, operating history of the battery pack, testing history of the first battery cell, testing history of the battery pack, SOC of the first battery cell, SOC of the battery pack, temperature of the first battery cell, OCV of the first battery cell, voltage of the first battery cell under a given load, or test data analysis of battery cells equivalent to the first battery cell.
4. The method of claim 1 , wherein the cell data comprises changes in an open circuit voltage (OCV) of the first battery cell over a time period, while the external cell current is discontinued through the first battery cell.
5. The method of claim 4 , wherein the time period is dynamically selected based on the changes in the OCV of the first battery cell.
6. The method of claim 1 , wherein reestablishing the external cell current through the first battery cell is performed when a state of charge (SOC) of the first battery cell corresponds to a SOC of at least one other battery cell in the battery pack.
7. The method of claim 1 , wherein reestablishing the external cell current through the first battery cell is performed after the at least one other battery cell in the battery pack has undergone one or more charge-discharge cycles, while the external cell current has been discontinued through the first battery cell.
8. The method of claim 1 , further comprising determining new operating parameters for the first battery cell based on the leakage current of the first battery cell, and wherein the external cell current through the first battery cell is reestablished according to the new operating parameters.
9. The method of claim 1 , further comprising determining one or more degradation mechanisms of the first battery cell based on at least the leakage current of the first battery cell.
10. The method of claim 9 , wherein determining the one or more degradation mechanisms of the first battery cell comprises comparing the leakage current of the first battery cell with different degradation signatures.
11. The method of claim 9 , wherein the one or more degradation mechanisms comprise at least one of an internal mechanical short, gas evolution, solid electrolyte interface, or metal dendrite formation.
12. The method of claim 9 , wherein the one or more degradation mechanisms is further determined based on at least one of: temperature of the first battery cell while discontinuing the external cell current through the first battery cell, SOC of the first battery cell when discontinuing the external cell current through the first battery cell, and operating history of the first battery cell before discontinuing the external cell current through the first battery cell.
13. The method of claim 1 , further comprising transmitting data representing the leakage current of the first battery cell from the battery pack to a battery data system, communicatively coupled to the battery pack.
14. The method of claim 1 , wherein the external cell current is discontinued through the first battery cell when the first battery cell is at a first state, wherein the in-situ leakage current testing of the first battery cell is repeated when the first battery cell is at a second state, different from the first state, and wherein the first state and the second state are differentiated by one of temperature of the first battery cell, SOC of the first battery cell, or prior operation history of the first battery cell.
15. The method of claim 4 , wherein the external cell current is discontinued through the first battery cell for a period of time selected based on at least one of the leakage current, desired test accuracy, equipment precision, a type of the first battery cell, temperature of the first battery cell, or a state of charge of the first battery cell.
16. The method of claim 1 , wherein the cell data, used for determining the leakage current, is a charge amount used by the first node controller to bring a state of charge of the first battery cell to an initial state of charge at which the external cell current was disconnected through the first battery cell.
17. The method of claim 1 , wherein the cell data, which is used for determining the leakage current, is a cell current used by the first node controller to maintain a selected state of charge over time.
18. The method of claim 2 , wherein the predetermined range of the state of charge is selected based on one or more degradation mechanisms.
19. The method of claim 14 , wherein the first state and the second state correspond to different degradation mechanisms.
20. The method of claim 8 , wherein the external cell current through the first battery cell, reestablished according to the new operating parameters, is less than a corresponding external current through at least one of the one or more additional cells in the battery pack.
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August 18, 2020
September 28, 2021
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